Method of electroerosion machining of parts and device for effecting same

ABSTRACT

A method and device for effecting electroerosion machining comprises a high-frequency source of pulses of a relatively low amplitude of current and a low-frequency source of pulses of a relatively high amplitude of current controlled by circuits for automatically switching over said sources in response to a decrease in the interelectrode gap value and for switching them back after a predetermined period of time. Alternatively a source of variable frequency of pulses of electric energy with a high amplitude of voltage may be employed with a pulse step-down transformer and circuits for automatic decrease of the frequency of the source and its direct connection with the electrodes for a predetermined period of time in response to a decrease in the interelectrode gap value, there being provided control elements for disconnecting the windings of the transformer and directly connecting the high-voltage source with the electrodes, and for restoration of the circuits after a predetermined period of time.

United States Patent Raznitsyn 51 June 20, 1972 [54] METHOD OFELECTROEROSION MACHINING OF PARTS AND DEVICE FOR EFFECTING SAME MikhailAlexeevich Raznitsyn, ul Arbat 54/2, kv. 83, Moscow, U.S.S.R.

[22] Filed: Aug. 12,1970

[21] Appl.No.: 63,296

[72] Inventor:

[58] Field ofSearch ..219/69 C, 69 R, 69 G, 69 P, 219/69 V [56]References Cited UNITED STATES PATENTS 3,213,258 10/1965 Ferguson..219/69 P Primary Examiner-R F. Staubly [5 7] ABSTRACT A method anddevice for effecting electroerosion machining comprises a high-frequencysource of pulses of a relatively low amplitude of current and alow-frequency source of pulses of a relatively high amplitude of currentcontrolled by circuits for automatically switching over said sources inresponse to a decrease in the interelectrode gap value and for switchingthem back after a predetermined period of time. Alternatively a sourceof variable frequency of pulses of electric energy with a high amplitudeof voltage may be employed with a pulse stepdown transformer andcircuits for automatic decrease of the frequency of the source and itsdirect connection with the electrodes for a predetermined period of timein response to a decrease in the interelectrode gap value, there beingprovided control elements for disconnecting the windings of thetransformer and directly connecting the high-voltage source with theelectrodes, and for restoration of the circuits after a predeterminedperiod of time.

8 Claims, 3 Drawing Figures Patented June 20, 1972 3,671,705

3 Sheets-Sheet 1 FIG. 1

D v 3 I shee she llllllllllllllllll IIIIIIIIIIIIII llllllllllll PatentedJune 20, 1972 3 Sheets-Sheet 3 This application is a continuation ofapplication Ser. No. 654, 836, filed July 20, 1967.

The present invention relatesto methods of electroerosion machining ofparts by pulses of discharge electric current and to devices foreffecting same.

The invention is intended to be used for tool production in variousbranches of industry.

Known in the prior art are methods of electroerosion machining of parts,to be effected by passing working pulses of discharge current throughelectrodes and by relative transfer of the electrodes along theprescribed trajectory in a follow-up mode of feed (see, for example,Manual of electric and ultrasonic methods of machining materials, byL.Ya.Popilov, Mashgiz, Moscow-Leningrad, 1963, page 250).

Also known in the prior art are devices for carrying into effect saidmethods of electroerosion machining, comprising electrodes, a generatorof working pulses, and a measuring instrument, connected in parallel,and a follow-up system for effecting a directed relative transfer ofelectrodes (see, for example, Automation of electric spark andanode-mechanical machine tools, Mashgiz,Moscow-Leningrad,1952, page 55).

The existing methods of electroerosion machining, however, have thedisadvantage that in case of a casual contact between the electrodes,the process of removing material from the part to be machined isdiscontinued, the pulse current density flowing through the areas ofactual contact being insufficient for their separation.

Therefore the existing devices for effecting said electroerosionmachining processes are designed so as to permit resuming of themachining process interrupted by the casual contact between theelectrodes by drawing apart the electrodes along the path they havecovered.

In case the working electrodes move along two or more coordinates in thecourse of their relative transfer, this peculiar feature considerablycomplicates the system of automatic control of the relative transferofthe electrodes, requiring their provision with an intermediate memoryfor effecting the non-programmed reversal of the working feed along thecovered trajectory and return to the earlier reached point.

An object of the present invention is to provide such a method ofelectroerosion machining of parts and a device for its realization,which permits the employment of standard systems used in automation ofmetal-cutting machines for the transfer control, to effect automaticcontrol of multiple-coordinate relative transfer of the workingelectrodes of the electroerosion machine tool.

In conformity withthe above and other objects, the essential. feature ofthe present invention consists in applying the method of electroerosionmachining of parts, bypassing working pulses of a discharge currentthrough electrodes and by relative'transfer of the electrodes along theprescribed trajectory in a mode of follow-up feed, in which, accordingto the invention, at the moment of a casualcontact between theelectrodes the latter are not brought apart, and auxiliary pulses ofcurrent are passed with an amplitude greater than that of theshort-circuit current for a period of time required to eliminatethecontact thus formed by virtue of the contact electric erosion.

It is advisable that for the time of passing the auxiliary pulses ofcurrent through the contacting electrodes the passing of the .workingimpulses be discontinued. In the device for effecting the method ofelectroerosion machining of parts, comprising electrodes, a generator ofworking pulses, a measuring instrument, and a follow-up system foreffecting directed relative transfer of the electrodes, according to theinvention, there is provided an auxiliary generator, connected to theelectrodes, and a master switch, connected to the measuring instrumentand auxiliary generator for actuating the latter with the arrival of asignal from the measuring instrument in caseof a casual contact betweenthe electrodes.

2 j It is expedient that the circuit of the measuring instrument andgenerator of working pulses keys be provided, connected to the masterswitch.

Other objects and advantages of the present invention will 7 become morefully apparent from a consideration of the following description ofexemplary embodiments thereof, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 represents a device and an electric circuit diagram of the devicewith an auxiliary generator, according to the present invention; i

FIG. 2 diagrammatically represents another embodiment of the electriccircuit of the device with the auxiliary'generator,

according to the present invention;

FIG. 3 represents still another embodiment of the electric circuit ofthe device, according to the present invention.

The device for the electroerosion machining of parts (FIG. 1) comprisesa two-coordinate table 1, driven by electric motors 2 and 3, said table1 mounting a workpiece-electrode 4 to be machined. Theworkpiece-electrode 4 and a tool-electrode 5 are connected to the outputof a generator 6 of working pulses through a controllable key 7. 1

Connected in parallel with the electrodes 4 and 5 via a controllable key8 is a measuring instrument 9 whichproduces signals to operate a system10 controlling the transfer of the electrodes, said system by drivingthe electric motors land 3, is operating in the mode of a follow-up feedensuring the stabilization of the interelectrode gap.

Connected in parallel with the generator 6 of working pulses is anauxiliary generator 11.. v

The measuring instrument 9 is connected to the master switch 12, whichactuates the auxiliary generator 11 and keys 7 and 8.

FIG. 2 represents an embodiment of the same device, in which, ascompared with the device shown in FIG. 1, the protection of thegenerator 6 of working pulses against the pulses of the auxiliarygenerator 11,.is effected in a different manner. In the circuit of thegenerator 6 of working pulses there is provided a diode l3 inhibitingthe pulses of the auxiliary generator ll getting to the generator'6 ofworking pulses and measuring instrument 9.

In the present embodiment of the invention, the actuation of the masterswitch 12 results only in the enabling of the auxwinding 17 is connectedto the workpiece-electrode 4 and 1 tool-electrode 5.

Connected in parallel with the secondary winding 17 of the transformer16 through a controllable key 18 is a measuring instrument 9', connectedwith a system 10' controlling the transfer and a master switch 12. Themaster switch 12 is, in its turn, connected to keys 19, 20, which, whe nthe master switch 12 is disabled, connect the electrodes 4 and 5 to thesecondary winding 17 of the transformer 16 and to keys 22 and 23'whichthen block the current. The master switch 12 is similar to that insertedin the circuit diagram shown in FIGS. 1 and 2.

The device, represented in FIG. 1, operates as follows.

The generator 6 of working pulses is kept permanently switched on andsupplies pulse voltage through the open key 7 to the electrodes 4 and 5.Thepresence of a preset gap between these electrodes provides for theformation of periodic pulse discharges therebetween, which results inthe removal of the material from the article or workpiece beingmachined, which is conducive to an increase in the gap The requiredtransfer occurs up to the moment when a decrease inthe magnitude of theinterelectrode gap (caused bythe relative transfer of the electrodes 4and 5) restores the required value of the control signal, fed by themeasuring instrument 9 to the follow-up system 10.

Thereafter the transfer motion is discontinued until the interelectrodegap increases again. In the course of this normal cycle of the deviceoperation, master switch 12 and auxiliary generator 11 are disconnected,while the keys 7 and 8 are actuated.

The master switch is adapted to control the operation of the keys 7 and8, as well as that of the auxiliary generator 11.

On the contrary, the disconnection of the master switch 12 opens thekeys 7 and 8, and disconnects the auxiliary generator l1.

The connection of the master switch 12 is caused by a certain level ofthe control signal coming from the measuring instrument 9.

Disconnecting of the master switch 12 occurs spontaneously after acertain period of time, which is preset by adjusting a time delayelement incorporated in its circuit (not shown in the drawing).

in the case of casual short-circuiting of the electrodes 4 and 5, whichmay be caused, for example, by foreign inclusions in the article orworkpiece being machined, the control signal, sent both into the system10 controlling the transfer for the directed relative transfer motion ofthe electrodes 4, 5, and into the master switch 12, changes to such anextent as to cause the working feed to cease, and connect the masterswitch 12, which, via the keys 7 and 8, opens the circuit of thegenerator 60f working pulses and that of the measuring instrument 9, andactuates the auxiliary generator 11. Current pulses of an increasedamplitude, fed by the auxiliary generator 11, when passing through acontact between the electrodes 4 and 5, cause the destruction of contactbridges therebetween, thus creating the required interelectrode gap.

On the elapse of the proper time delay for self-disconnection, themaster switch 12 is disconnected,-thus restoring the original electriccircuit and disconnecting auxiliary generator 11. 1

In the case the interelectrode gap is formed,'the signal, received fromthe measuring instrument 9 after the master switch 12 has beendisconnected, possesses characteristics, which do not cause the repeatedcutting in of the master switch 12 so that the normal process ofmachining is continued ensured by the generator 6 of working pulses andthe system 10 controlling the transfer. d

If no interelectrode gap has been created during the operation of theauxiliary generator, the restoring of theelectric circuit caused by thedisconnection of the masterswitch, will make a signal, corresponding tothe contact between the electrodes 4 and 5, to be sent from themeasuring instrument 9 to the master switch, this resulting in themaster switch being enabled again for a certain period of time.

The auxiliary generator 11 will be switched in again accordingly tillthe contact between the electrodes is eliminated. The device representedin FIG. 3 operates in the following manner.

High-voltage charging current from the generator 6' of working pulsescharges a capacitor 14. The charging having been completed, thethyratron 15 is opened, the capacitor 14 is discharged through theprimary winding 21 of the transformer 16, thus'creating a decreasedpulse voltage at its secondary winding 17 connected to the electrodes 4and 5, said voltagecauses a pulse discharge between the latter.

i The capacitor 14 having been discharged, the thyratron 15 I is closed,and a new charging cycle of the capacitor 14 commences. These cyclesfollow each other at a high frequency,

thus causing a high-frequency electroerosion process betweenterelectrode gap. The master switch l2 is thereby disconnected, and thelevel of signal received from the. measuring instrument 9'- proves to beinsufficient for its cutting in. In the case of a casual short-circuitbetween the electrodes 4, 5, the signal from the measuring instrument 9'interrupts the sending of signals from the system 10 controlling thetransfer to the electric motors 2 and 3 and enables the master switch12, which disables the key 18, disconnecting thereby the circuit of themeasuring instrument 9', disables the keys 19 and 20, and enables thekeys 22 and 23, which causes the disconnection of the primary winding 21and secondary winding 17 of the output transformer 16 and provides forconnecting the electrodes 4 and 5 directly tothe output of the generator6 of working pulses.

Simultaneously the frequency of the generator 6' of working pulses isswitched over to preserve the average value of current flowing throughthe thyratron 15. I

The short-circuited electrodes 4, 5 cause the high-voltage dischargecircuitto be closed.

The current in the circuit is limited only by the natural resistance ofthe thyratron l5. Currentpulses of an amplitude thus increased passthrough the electrodes 4 and 5, breaking contact bridges therebetweenand creating the required gap. The protection of the thyratron 15 isensured owing to a decrease in thefrequency of generated pulses.

Though the present invention is described in connection with a preferredembodiment thereof, it is obvious that modifications and alternationsare possible without departing from the true idea and scope of theinvention, as those skilled in the art will easily understand.

Iclaim:

l. A method of electroerosion machining comprising .supplying periodicpulses of electric energy with a relatively highfrequency andcomparatively small amplitude of current from an intermittent currentsource to a gap between a-tool and a work-piece serving as electrodes,displacing the tool relative.

to the work-piece at a controlled speed in forward-stop operatingconditions, supplying to the gap periodic pulses of electric energy witha comparatively high amplitude of current of a relatively low-frequencysimultaneously with said highan intermittent current source to a gapbetween a tool and a work-piece serving as electrodes, displacing thetool relative to the work-piece at a controlled speed in forward-stopoperating conditions, discontinuing the application of the pulses andthe relative movement of the electrodes during a predetermined timeperiod in which said gap is non-existent and the electrodes are incontact with one another, while supplying the gap with periodic pulsesof electric energy with a relatively low-frequency and comparativelyhigh amplitude of current, restoring the gapto its predetermined value,and discontinuing the supply of the low-frequency pulses and resupplyingthe high-frequency pulses and resuming the rela; tive movement of theelectrodes when the predetermined workpiece constituting electrodes,meansfor displacing the tool relative to the workpiece along-apredetennined trajectory at a controlled speed in forward-stop operatingconditions, and means for selectively feeding to said tool and workpieceshort periodic pulses of energy of a relatively high-frequency with acomparatively'low amplitude of current and in a predetermined period oftime when the gap is non-existent short periodic pulses of energy of arelatively low-frequency with a comparatively high amplitude of current.

4. A device for electroerosion machining comprising a tool disposed witha gap relative to a workpiece, said tool and workpiece constitutingelectrodes, means for displacing the tool at a controlled speed in aforward-stop operating condition, a supply source of periodichigh-frequency pulses of a relatively small amplitude of current; andmeans automatically actuated in response to a decrease of the value ofthe gap to zero to apply, across said gap, in a predetermined period oftime periodic low-frequency pulses of a relatively high amplitude ofcurrent.

5. A device for electroerosion machining comprising a tool disposed witha gap relative to a workpiece, said tool and workpiece constitutingelectrodes, means for displacing the tool relative to the workpiecealong a predetermined trajectory at a controlled speed in a forward-stopoperating condition, a supply source of periodic high-frequency pulsesof a relatively small amplitude of current connected to said electrodesfor producing pulse discharges across said gap, means for applyingperiodic low-frequency pulses of .a relatively high amplitude of currentto said electrodes and across the gap when its value is zero; and meansautomatically actuated with a predetermined delay in time in response toactuation of the first said means to discontinue, after a predeterminedperiod of time, the supply across the gap of the relatively lowfrequencyperiodic pulses of energy and start again the supply across the gap onlyof the periodic relatively high-frequency pulses of energy with thecomparatively low amplitude of current.

6. A device for electroerosion machining comprising a tool spaced with agap relative to a workpiece; said tool and workpiece constitutingelectrodes; a source of periodic pulses, for producing across said gap,pulses of energy of a relatively high-frequency with a comparatively lowamplitude of current to carry out electroerosion machining; a source ofperiodic pulses, for producing across said gap, pulses of energy of arelatively low-frequency with a comparatively high amplitude of currentfor carrying out electroerosion machining when the value of theinterelectrode gap is zero and the electrodes are in contact with oneanother; control circuits for switching on said source of low-frequencypulses with high amplitude of current in response to a decrease of theinterelectrode gap to zero and for switching it off after apredetermined period of time; and a diode for separating the circuits ofboth' said sources of periodic pulses of energy.

7. A device for electroerosion machining comprising a tool spaced with agap relative to a workpiece; said tool and workpiece constitutingelectrodes, a source of periodic pulses, for producing across said gap,pulses of energy of a relatively high-frequency and a comparatively lowamplitude of current for carrying out electroerosion machining; a sourceof periodic pulses, for producing across said gap, pulses of energy of arelatively low-frequency and a comparatively high amplitude of currentfor carrying out electroerosion machining when the value of theinterelectrode gap is zero and the electrodes are in contact with oneanother; control circuits for disconnecting from the electrodes thesource of pulses of highfrequency and low amplitude of current andconnecting to the electrodes the source of pulses of low-frequency andhigh amplitude of current in response to a decrease of theinterelectrode gap to zero, and for switching off the source of pulsesof low-frequency and high amplitude of current and switching on thesource of pulses of high-frequency and low amplitude of current after apredetermined period of time; and a commutating element controlling saidcontrol circuits for connecting and disconnecting the electrodes withsaid sources of pulses.

8. A device for electroerosion machining comprising a tool spaced with agap relative to a workpiece; said tool and workpiece constitutingelectrodes; a source of periodic pulses of energy with a variablefrequency and a high amplitude of voltage; a pulse step-down transformerfor decreasing the voltage of the pulses of energy supplied to theelectrodes; a control circuit for automatically switching off saidtransformer and decreasing the frequency of periodic pulses of thesource in response to a decrease of the value of the interelectrode gapbelow a predetermined value and for restoring, after a predeterminedperiod of time, the connection of said transformer and the frequency ofthe periodic pulses of the source, a commutating element controllingsaid control circuit and inserted in the circuits of the primary andsecondary windings of said transformer to automatically break saidprimary and secondary windings of the transformer and connect the sourceof the pulses of high voltage with the electrodes in response to theactuation of said control circuit and to restore the connection of saidcircuits of the transformer in response to the switching-off of thecontrol circuits after a predetennined period of time.

1. A method of electroerosion machining comprising supplying periodicpulses of electric energy with a relatively highfrequency andcomparatively small amplitude of current from an intermittent currentsource to a gap between a tool and a workpiece serving as electrodes,displacing the tool relative to the work-piece at a controlled speed inforward-stop operating conditions, supplying to the gap periodic pulsesof electric energy with a comparatively high amplitude of current of arelatively low-frequency simultaneously with said high-frequency pulsesduring a predetermined time period in which said gap is non-existent andthe electrodes are in contact with one anothEr, restoring the gap to itspredetermined value, and, discontinuing the supply of the low-frequencypulses and resuming the relative movement of the electrodes after thepredetermined value of the gap is restored.
 2. A method ofelectroerosion machining comprising supplying periodic pulses ofelectric energy with a relatively high frequency and comparatively smallamplitude of current from an intermittent current source to a gapbetween a tool and a work-piece serving as electrodes, displacing thetool relative to the work-piece at a controlled speed in forward-stopoperating conditions, discontinuing the application of the pulses andthe relative movement of the electrodes during a predetermined timeperiod in which said gap is non-existent and the electrodes are incontact with one another, while supplying the gap with periodic pulsesof electric energy with a relatively low-frequency and comparativelyhigh amplitude of current, restoring the gap to its predetermined value,and discontinuing the supply of the low-frequency pulses and resupplyingthe high-frequency pulses and resuming the relative movement of theelectrodes when the predetermined value of the gap is restored.
 3. Adevice for electroerosion machining comprising a tool disposed with agap relative to a workpiece, said tool and workpiece constitutingelectrodes, means for displacing the tool relative to the workpiecealong a predetermined trajectory at a controlled speed in forward-stopoperating conditions, and means for selectively feeding to said tool andworkpiece short periodic pulses of energy of a relatively high-frequencywith a comparatively low amplitude of current and in a predeterminedperiod of time when the gap is non-existent short periodic pulses ofenergy of a relatively low-frequency with a comparatively high amplitudeof current.
 4. A device for electroerosion machining comprising a tooldisposed with a gap relative to a workpiece, said tool and workpiececonstituting electrodes, means for displacing the tool at a controlledspeed in a forward-stop operating condition, a supply source of periodichigh-frequency pulses of a relatively small amplitude of current; andmeans automatically actuated in response to a decrease of the value ofthe gap to zero to apply, across said gap, in a predetermined period oftime periodic low-frequency pulses of a relatively high amplitude ofcurrent.
 5. A device for electroerosion machining comprising a tooldisposed with a gap relative to a workpiece, said tool and workpiececonstituting electrodes, means for displacing the tool relative to theworkpiece along a predetermined trajectory at a controlled speed in aforward-stop operating condition, a supply source of periodichigh-frequency pulses of a relatively small amplitude of currentconnected to said electrodes for producing pulse discharges across saidgap, means for applying periodic low-frequency pulses of a relativelyhigh amplitude of current to said electrodes and across the gap when itsvalue is zero; and means automatically actuated with a predetermineddelay in time in response to actuation of the first said means todiscontinue, after a predetermined period of time, the supply across thegap of the relatively low-frequency periodic pulses of energy and startagain the supply across the gap only of the periodic relativelyhigh-frequency pulses of energy with the comparatively low amplitude ofcurrent.
 6. A device for electroerosion machining comprising a toolspaced with a gap relative to a workpiece; said tool and workpiececonstituting electrodes; a source of periodic pulses, for producingacross said gap, pulses of energy of a relatively high-frequency with acomparatively low amplitude of current to carry out electroerosionmachining; a source of periodic pulses, for producing across said gap,pulses of energy of a relatively low-frequency with a comparatively highamplitude of current for carrying out electroerosion machining when thevalue of the interelectrode gap is zero And the electrodes are incontact with one another; control circuits for switching on said sourceof low-frequency pulses with high amplitude of current in response to adecrease of the interelectrode gap to zero and for switching it offafter a predetermined period of time; and a diode for separating thecircuits of both said sources of periodic pulses of energy.
 7. A devicefor electroerosion machining comprising a tool spaced with a gaprelative to a workpiece; said tool and workpiece constitutingelectrodes, a source of periodic pulses, for producing across said gap,pulses of energy of a relatively high-frequency and a comparatively lowamplitude of current for carrying out electroerosion machining; a sourceof periodic pulses, for producing across said gap, pulses of energy of arelatively low-frequency and a comparatively high amplitude of currentfor carrying out electroerosion machining when the value of theinterelectrode gap is zero and the electrodes are in contact with oneanother; control circuits for disconnecting from the electrodes thesource of pulses of high-frequency and low amplitude of current andconnecting to the electrodes the source of pulses of low-frequency andhigh amplitude of current in response to a decrease of theinterelectrode gap to zero, and for switching off the source of pulsesof low-frequency and high amplitude of current and switching on thesource of pulses of high-frequency and low amplitude of current after apredetermined period of time; and a commutating element controlling saidcontrol circuits for connecting and disconnecting the electrodes withsaid sources of pulses.
 8. A device for electroerosion machiningcomprising a tool spaced with a gap relative to a workpiece; said tooland workpiece constituting electrodes; a source of periodic pulses ofenergy with a variable frequency and a high amplitude of voltage; apulse step-down transformer for decreasing the voltage of the pulses ofenergy supplied to the electrodes; a control circuit for automaticallyswitching off said transformer and decreasing the frequency of periodicpulses of the source in response to a decrease of the value of theinterelectrode gap below a predetermined value and for restoring, aftera predetermined period of time, the connection of said transformer andthe frequency of the periodic pulses of the source, a commutatingelement controlling said control circuit and inserted in the circuits ofthe primary and secondary windings of said transformer to automaticallybreak said primary and secondary windings of the transformer and connectthe source of the pulses of high voltage with the electrodes in responseto the actuation of said control circuit and to restore the connectionof said circuits of the transformer in response to the switching-off ofthe control circuits after a predetermined period of time.